Xanthophyll esters belong to the group of natural compounds known as carotenoids and are widely distributed in nature. They are fatty acid esters (e.g., palmitate and myristate esters) of such carotenoids as lutein and zeaxanthin. Zeaxanthin ester is the pigment contained in berries such as those of genus Lycium and Physalis. Lutein ester is the pigment that gives the yellow/red color to fruits such as oranges, peaches, papayas, prunes, and mangos. Lutein esters are also present in many flowers, particularly marigold flowers of genus Tagetes. Xanthophyll esters are generally found in nature as the trans-xanthophyll geometric isomer.
The marigold flower is the richest source of trans-lutein ester found in nature. Dried and ground marigold flowers have been used commercially since 1966 as botanical ingredients in animal feeds, and since 1969 as starting materials for the production of marigold extracts, which contain xanthophyll esters as the commercially important component, see e.g., Lackey, German Patent No. 1,224,597; Levy et al., Ecuadorean Patent No. 44. Marigold extracts are products of international commerce. They are used as pigmenting agents in animal feed formulations and as food coloring agents such as the European natural color E161b/lutein, see e.g., Levy et al., Ecuadorean Patent No. 44; Rosenberg, U.S. Pat. No. 3,539,686; Official Journal of the European Communities No. L-226/37.
Recent scientific research has shown that marigold extracts may be used as human nutritional supplements, based on important biological functions of lutein in humans such as prevention of cancer and prevention of a condition known as age-related degeneration of the macula of the human eye, among other possible uses of lutein esters in nutrition and medicine, see e.g. Chew et al., Anticancer Research, 16:3689 (1996); Marchand et al., "An Ecological Study of Diet and Lung Cancer in the South Pacific," International Journal of Cancer, 63:18-23 (1995); Park et al., "The Effect of Dietary Lutein on Growth of Mammary tumor in BALB/c Mice," The FASEB Journal, 11:2586 (1997); H. P. Kim et al., "Hepatoprotective Action of Zeaxanthin Palmitate from Lycium chinense," Research Communications Molecular Pathology and Pharmacology, 97:301-314 (1997); Landrum et al., Experimental Eye Research, 65:1:57 (1997). To be suitable for these important new applications in humans, marigold extracts must satisfy more stringent quality requirements than were necessary in the past.
For use in human nutritional supplements, xanthophyll ester concentrates must be essentially free of pesticide contamination. They should contain the xanthophyll ester in sufficiently high concentration, e.g., at least 40 wt. %, to allow for formulation into capsules and tablets, although lower concentrations may still be satisfactory for use as a nutritional supplement. To achieve the maximum possible bioavailability for xanthophyll-containing nutritional supplements, the xanthophylls should be present in their naturally-occurring ester form, not in saponified (i.e., free alcohol or diol) form, and the naturally-occurring trans-xanthophyll isomer should predominate, see e.g., Herbst et al., FASEB J. Abstract 11:2587 (1997); Johnson et al., J. Nutrition 127:1993 (1997).
Unfortunately, known commercial marigold extracts fail to meet one or more of these quality criteria. The largest producers of marigold extracts (companies in Peru, Mexico and Ecuador) produce extracts containing between 14 and 20 wt. % lutein ester, mainly for animal feed formulations. Inexa, Industria Extractora C.A. of Quito, Ecuador, also produces a superior grade containing about 35 wt. % lutein ester as a food color. Typically, these products have a large presence of non-xanthophyll lipids which are extracted from the plant material with the xanthophylls when standard extraction techniques are employed. Moreover, commercial lutein ester concentrates also usually contain about 20 to 30 wt. % of the total lutein ester in the cis-isomeric form, again due to standard conditions of industrial processing.
Finally, known lutein ester concentrates often contain residues of pesticides, which are introduced into xanthophyll-containing plant matter through common cultivation techniques, such as those used on marigold plantations, and are extracted along with xanthophyll esters by standard extraction processes. All of this makes the currently available commercial lutein ester concentrates unsuitable for use as human nutritional supplements.
Several different methods have been proposed in order to overcome these disadvantages. U.S. Pat. No. 4,048,203 of Philip describes the extraction of lutein esters from plant material, and further purification of the esters using alcohol at 75.degree. C. However, this heat treatment results in an undesirably large proportion of the less-bioavailable cis-xanthophyll isomer in the final product. See Comparative Example 1 below.
U.S. Pat. No. 5,382,714 of Khachik describes a process for the isolation, purification, and recrystallization of lutein from saponified marigold oleoresin, and U.S. Pat. No. 5,648,564 of Ausich et al. describes a process for the extraction, isolation, and purification of comestible xanthophyll crystals from plants. However, neither of these processes produces xanthophylls in their natural, most bioavailable, ester form because they both require a saponification step, whereby the natural xanthophyll ester form present in the plant material is destroyed.
U.S. Pat. No. 4,105,855 of Schulz teaches a method for synthesizing symmetrical carotenoids, which may be esters in all-trans isomeric form. However, lutein is not a symmetrical carotenoid, and while zeaxanthin is symmetrical, the only ester of zeaxanthin mentioned by Schulz is the diacetate as a last intermediate step in obtaining the diol. Schulz does not teach the synthesis or extraction of xanthophyll palmitate and myristate esters or their concentrates.
Thus, it is evident that there is a need in the art for a method of producing, through extraction and purification of plant material, xanthophyll concentrates that have enhanced purity and contain predominantly trans-xanthophylls in their natural ester form.